1. Field of the Invention
The present invention relates to rotary type electronic parts such as rotary type variable resistors and rotary switches.
2. Description of the Prior Art
As an example of volume controls, in which a heart-shape cam and a variable resistor are combined and reciprocating operation of its operating shaft and rotational operation of its sliding member are enabled, there is for example one as indicated in FIG. 6.
FIG. 6 is a cross-sectional view of a rotary type variable resistor (hereinafter to be referred to as a volume) of the prior art. Referring to the drawing, the volume control primarily consists of a variable resistor portion 1, cam portion 2, and an operating shaft 4 which passes through the variable resistor portion 1 and engages with a heart-shape cam member 3 (hereinafter to be referred to as a heart cam) of the cam portion 2.
The variable resistor portion 1 is provided, between its front plate 5 and back plate 6, with two substrates 8a, 8b, which are provided thereon with conductive patterns 7 as devices on the stationary side, a slider retainer 10 disposed between the substrates 8a, 8b for retaining, on its surface facing the conductive patterns 7 formed on the substrate 8a, 8b, sliders 9 as devices on the rotary side in slidable contact with the mentioned conductive patterns 7, and a fastening plate 12 engaged with an axial portion 10a of the slider retainer 10 for transmitting rotation of the operating shaft 4 thereto and, at the same time, supporting an annular plate spring 11 for providing rotating torque, and these are integrated by pins, not shown, passed therethrough and caulked, with the distance between the substrates 8a, 8b regulated by the side plates 13a, 13b. Denoted by 14 are terminals connected with the conductive patterns 7.
The cam portion 2 consists of a housing 15, front plate 16 on the side of the variable resistor portion 1, heart cam 3 housed in the housing 15 and normally urged in the direction of the front plate 16 by a spring 17, engagement pin 18 projecting from the side of the front plate 16, the tip of the engagement pin 18 being adapted to move along a cam groove 20 of the heart cam 3, and a plate spring 19 elastically pressing the engagement pin 18 in the direction of the cam groove 20.
The heart cam 3 is provided with a cam groove 20 cut in the undersurface, and it is adapted such that a predetermined reciprocating motion of the operating shaft 4 is completed by means of a stepped portion provided in the cam groove 20 while the tip of the engagement pin 18 makes a round of the cam groove 20. In the end face of the heart cam 3, there is cut an engagement groove 21 with which the groove portion 4a at the tip of the operating shaft 4 is adapted to elastically engage as shown in FIG. 8, and the inlet side for the engagement opens on the groove 16a cut in the front plate 16.
With the volume as structured above, the position indicated in FIG. 4 is where the operating shaft 4 is rotatable. After the volume is adjusted to a desired volume level there, if the operating side 4b of the operating shaft 4 is pushed in the direction indicated by the arrow A, the tip portion 18a of the engagement pin 18 is introduced into the cam groove 20 from the position B through the inlet portion 20a of the cam groove 20. The tip then moves along the inward passage 20b of the cam groove 20 in the direction indicated by the arrow C, and when the push is released after the operating shaft 4 has been pushed a full stroke, the same moves along the passage indicated by the arrow D and reaches the engagement position E and the heart cam 3 stops at this position E, whereby the operating shaft 4 also stops in the position as pushed in toward the front plate 5. As a result, operating parts provided on the operating side 4b of the operating shaft 4 such as a knob are received within the main body, and so, the knob and other parts can be put out of the way while the same are not in use. If the operating side 4b of the operating shaft 4 is pushed in from this position, the tip portion 18a of the pin 18 moves in the direction as indicated by the arrow F, and when the push is released, the same moves along the outward passage 20c in the direction indicated by the arrow G and returns to the position B through the inlet portion 20a, whereby the heart cam 3 restores the position indicated by FIG. 6 to enable the rotary operation of the operating shaft 4. Incidentally, FIG. 9 shows that the tip portion 18a of the pin 18 would move about, but, of course, this is just for explanation; in reality, the tip portion 18a of the pin 18 is only allowed to swing about the fitted position 18b of the pin 18 in the direction perpendicular to the surface of the paper of FIG. 7, and so, the heart cam 3 makes the reciprocating movement with reference to the pin 18 to perform the above described function.
In the case where the volume structured as described above is assembled, the variable resistor portion 1 and the cam portion 2 are separately assembled in advance. Thereafter, the groove portion 4a of the operating shaft 4 projecting out of the variable resistor portion 1 is put in engagement with the engagement groove 21 of the heart cam 3, and then the variable resistor portion 1 is integrated with the cam portion 2 by means of pins or the like, not shown, and thus the assembling is finished. More particularly, the mentioned groove portion 4a is inserted into the groove 16a cut in the front plate 16 from above at an angle, as indicated in FIG. 7, in the direction indicated by the arrow I, so that the same is inserted into the engagement groove 21 of the heart cam 3 and put in elastic engagement with the engagement groove 21. At this time, since the spring 17 is abutting on the rear side of the heart cam 3, the insertion must be made while the spring 17 is pushed back. This engagement is effected by elastic deformation of the end face portion of the heart cam 3 in the circumferential direction.
The volumes structured as above, however, are more frequently used for small-sized apparatus as car audio equipment, for example, and so, the component parts for such a volume becomes still smaller. Therefore, there was a problem of deteriorated efficiency in the assembly work by the employment of the described assembling method, in which the groove 4a has to be inserted into the engagement groove 21 from above at an angle with the spring 17 pushed back.